Drops, Bubbles and Wetting in Helium

氦气中的液滴、气泡和润湿

• 批准号: 0907495
• 负责人: Peter Taborek
• 金额: $ 66万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0907495&HistoricalAwards=false
• 关键词: Drops; Bubbles; Wetting; Helium

****NON-TECHNICAL ABSTRACT****Atoms near a solid surface experience a long range attractive force. Long range forces between molecules are important because they determine macroscopic properties of matter; such as what phase (solid, liquid, gas, etc) is stable at a given temperature and the friction between sliding surfaces. Long range forces also determine the shape of large biologically important molecules such as proteins and DNA. This individual investigator award supports project designed to measure long range forces in some simple model systems using several complementary methods. One method is to expose a solid to a gas and then weigh the amount of adsorbed gas on the surface using a microbalance that can detect fractions of a single atomic layer. Atoms adsorbed on a surface can be considered to be two dimensional matter. They undergo phase transitions such as vaporization and freezing, which are very similar to the familiar three dimensional counterparts. When the adsorbed atoms are very light and weakly interacting (e.g. helium), quantum mechanical effects become important and the adsorbed 2D liquid can also become a superfluid, which means that it can flow forever without any driving force. Theory suggests that for helium-4 on substrates of alkali metals (lithium, sodium, potassium, etc) there are unusual competitions between the liquid-vapor transition and the superfluid-normal fluid transition. This competition will be investigated using both microbalances and reflection of polarized light. Another way to measure surface forces is to use an atomic force microscope (AFM). The forces are measured by monitoring the deflection of a micromachined silicon cantilever with a laser when the cantilever is brought near the surface. Making these measurements with a cantilever immersed in liquid helium is technically challenging, and is one of the goals of this project. Students and post doctoral associates involved with this project will have the opportunity to develop novel instruments, and receive training in a broad spectrum of techniques including cryogenics, high speed imaging, laser optics, and materials preparation. This training will enable them to become productive members of the research community, whether in academia, industrial or government laboratories.****TECHNICAL ABSTRACT****This award supports an individual investigator project with several aims in the general area of fluids, predominately quantum fluids. Wetting and its relationship to superfluid phase transitions when films of helium and helium mixtures are adsorbed on weak and intermediate strength alkali metal and metal oxide substrates will be studied and compared with theory. For another study, low temperature atomic force microscope (AFM) techniques will be developed. The AFM will be optimized to enable measurement of the distance dependence of Casimir forces due to both fluctuations in the electromagnetic field and fluctuations in the order parameter near the onset of superfluidity. Finally a smaller project will investigate the pinch-off phenomena in drops and bubbles to elucidate the connections between the phenomena in conventional viscous fluids and non-Newtonian fluids. The computer code developed for the pinch-off studies will be adapted to study the stability and breakup of multi-electron drops in Helium. Furthermore the motion of superfluid droplets on non-wetting surfaces will be studied. Students and post doctoral associates involved with this project will have the opportunity to develop novel instruments, and receive training in a broad spectrum of techniques including cryogenics, high speed imaging, laser optics, and materials preparation. This training will enable them to become productive members of the research community, whether in academia, industrial or government laboratories.

* 非技术性摘要 * 靠近固体表面的原子受到一种长距离的吸引力。分子间的长程力很重要，因为它们决定了物质的宏观性质，例如在给定温度下什么相（固体、液体、气体等）是稳定的，以及滑动表面之间的摩擦。 长程力也决定了生物学上重要的大分子如蛋白质和DNA的形状。 这个个人研究者奖支持的项目旨在使用几种互补的方法在一些简单的模型系统中测量长距离力。一种方法是将固体暴露于气体中，然后使用可以检测单个原子层的分数的微量天平来称量表面上吸附的气体的量。 吸附在表面上的原子可以被认为是二维物质。 它们经历相变，如蒸发和冻结，这与熟悉的三维对应物非常相似。 当被吸附的原子非常轻并且相互作用很弱（例如氦）时，量子力学效应变得很重要，被吸附的2D液体也可以成为超流体，这意味着它可以在没有任何驱动力的情况下永远流动。 理论表明，氦-4在碱金属（锂、钠、钾等）基质上，在液体-蒸气转变和超流体-正常流体转变之间存在着不寻常的竞争。 将使用微量天平和偏振光反射来研究这种竞争。 测量表面力的另一种方法是使用原子力显微镜（AFM）。当悬臂靠近表面时，通过用激光监测微机械加工的硅悬臂的偏转来测量力。 用浸没在液氦中的悬臂进行这些测量在技术上具有挑战性，这也是该项目的目标之一。 参与该项目的学生和博士后将有机会开发新型仪器，并接受广泛的技术培训，包括低温学，高速成像，激光光学和材料制备。 这种培训将使他们成为研究界的富有成效的成员，无论是在学术界，工业界还是政府实验室。技术摘要 **** 该奖项支持个人研究项目，在流体，主要是量子流体的一般领域有几个目标。 将研究氦和氦混合物薄膜吸附在弱强度和中等强度碱金属和金属氧化物衬底上时的润湿及其与超流相变的关系，并与理论进行比较。 在另一项研究中，将开发低温原子力显微镜（AFM）技术。 原子力显微镜将进行优化，使测量的Casimir力的距离依赖性，由于在电磁场的波动和波动的序参数附近的超流性的发病。 最后，一个较小的项目将研究液滴和气泡中的夹断现象，以阐明传统粘性流体和非牛顿流体中的现象之间的联系。 为夹断研究开发的计算机代码将适用于研究氦中多电子液滴的稳定性和破裂。 此外，超流液滴在非润湿表面上的运动也将被研究。 参与该项目的学生和博士后将有机会开发新型仪器，并接受广泛的技术培训，包括低温学，高速成像，激光光学和材料制备。 这种培训将使他们成为研究界的富有成效的成员，无论是在学术界，工业界还是政府实验室。